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.TH SEM_TIMEDWAIT 3C "Feb 5, 2008"
.SH NAME
sem_timedwait, sem_reltimedwait_np \- lock a semaphore
.SH SYNOPSIS
.LP
.nf
#include <semaphore.h>
#include <time.h>

\fBint\fR \fBsem_timedwait\fR(\fBsem_t *restrict\fR \fIsem\fR,
     \fBconst struct timespec *restrict\fR \fIabs_timeout\fR);
.fi

.LP
.nf
\fBint\fR \fBsem_reltimedwait_np\fR(\fBsem_t *restrict\fR \fIsem\fR,
     \fBconst struct timespec *restrict\fR \fIrel_timeout\fR);
.fi

.SH DESCRIPTION
.LP
The \fBsem_timedwait()\fR function locks the semaphore referenced by \fIsem\fR
as in the \fBsem_wait\fR(3C) function. However, if the semaphore cannot be
locked without waiting for another process or thread to unlock the semaphore by
performing a \fBsem_post\fR(3C) function, this wait is terminated when the
specified timeout expires.
.sp
.LP
The \fBsem_reltimedwait_np()\fR function is identical to the
\fBsem_timedwait()\fR function, except that the timeout is specified as a
relative time interval.
.sp
.LP
For \fBsem_timedwait()\fR, the timeout expires when the absolute time specified
by \fIabs_timeout\fR passes, as measured by the \fBCLOCK_REALTIME\fR clock
(that is, when the value of that clock equals or exceeds \fIabs_timeout\fR), or
if the absolute time specified by \fIabs_timeout\fR has already been passed at
the time of the call.
.sp
.LP
For \fBsem_reltimedwait_np()\fR, the timeout expires when the time interval
specified by \fIrel_timeout\fR passes, as measured by the \fBCLOCK_REALTIME\fR
clock, or if the time interval specified by \fIrel_timeout\fR is negative at
the time of the call.
.sp
.LP
The resolution of the timeout is the resolution of the \fBCLOCK_REALTIME\fR
clock. The \fBtimespec\fR data type is defined as a structure in the
<\fBtime.h\fR> header.
.sp
.LP
Under no circumstance does the function fail with a timeout if the semaphore
can be locked immediately. The validity of the \fIabs_timeout\fR need not be
checked if the semaphore can be locked immediately.
.SH RETURN VALUES
.LP
The \fBsem_timedwait()\fR and \fBsem_reltimedwait_np()\fR functions return 0 if
the calling process successfully performed the semaphore lock operation on the
semaphore designated by \fIsem\fR. If the call was unsuccessful, the state of
the semaphore is be unchanged and the function returns -1 and sets \fBerrno\fR
to indicate the error.
.SH ERRORS
.LP
The \fBsem_timedwait()\fR and \fBsem_reltimedwait_np()\fR functions will fail
if:
.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 13n
The \fIsem\fR argument does not refer to a valid semaphore.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 13n
The process or thread would have blocked, and the timeout parameter specified a
nanoseconds field value less than zero or greater than or equal to 1,000
million.
.RE

.sp
.ne 2
.na
\fB\fBETIMEDOUT\fR\fR
.ad
.RS 13n
The semaphore could not be locked before the specified timeout expired.
.RE

.sp
.LP
The \fBsem_timedwait()\fR and \fBsem_reltimedwait_np()\fR functions may fail
if:
.sp
.ne 2
.na
\fB\fBEDEADLK\fR\fR
.ad
.RS 11n
A deadlock condition was detected.
.RE

.sp
.ne 2
.na
\fB\fBEINTR\fR\fR
.ad
.RS 11n
A signal interrupted this function.
.RE

.SH ATTRIBUTES
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	MT-Safe
_
Standard	See below.
.TE

.sp
.LP
For \fBsem_timedwait()\fR, see \fBstandards\fR(7).
.SH SEE ALSO
.LP
.BR semctl (2),
.BR semget (2),
.BR semop (2),
.BR time (2),
.BR sem_post (3C),
.BR sem_trywait (3C),
.BR sem_wait (3C),
.BR attributes (7),
.BR standards (7)
